1. Field of the Invention
The present invention relates to an electric beam tester which tests electric components such as a semiconductor. In particular, the present invention relates to an electric beam tester which has a means of correcting an image scanned by an electric beam.
2. Description of the Related Art
If a magnetic field is generated in an electric component, which is an object being measured by an electric beam tester, an error is generated at the landing point of the primary electron. Distortion therefore occurs in the measuring results of the voltage waveform. To correct this distortion, Logic State Mapping image, LSM image is used. The LSM image is an image obtained by providing a test pattern to electric components such as semiconductors and at the same time scanning the electric components. The error of the landing point of the primary electron can be measured by measuring the change of the LSM image with time. By previously measuring the error of the landing point of the primary electrons, the necessary correction can be made to each phase of the test signal, even in the case of measuring the voltage waveform of the electric component.
FIG. 1 shows an example of the LSM image. It is desirable to automatically calculate the magnitude of the landing point error of the primary electron based on the LSM image. However, there is an area in the LSM image in which the secondary electron is not detected as shown in the black areas in FIG. 1. Furthermore, because a pattern or wiring such as GND and power supply, are cut off in the upper and lower edges of the LSM image, it is difficult to calculate the degree of deviation just using the simple operation method. Additionally, because the signal to noise ratio, SN ratio, of the LSM image data is low, it is difficult to calculate the degree of deviation just using the simple operation method. Therefore, it is difficult to automatically calculate the magnitude of the landing point error of the primary electron.
Thus, the operator of the electric beam tester detects the degree of deviation by referring to the LSM image, and corrects the landing point of the primary electrons according to the degree of deviation. Therefore, the problem can occur where the degree of deviation cannot be accurately detected, and a complicated operation has to be undertaken for the correction.